Creating a learning health system to improve child health will require a new generation of researchers whose work is more directly aligned with the expressed needs of patients, providers, and healthcare systems. The evidence base they create, using child (and family) centered comparative effectiveness methods, will inform decisions of patients and providers that affect not only immediate health outcomes, but also long term life course trajectories. They will also conduct research on implementation and dissemination of practices that reliably improve health and wellbeing in a wide range of contexts, in order to benefit all children, and to reduce the persistent disparities seen in child health by race, ethnicity, and social class. Our proposed career development program leverages a broad and diverse Harvard faculty with 2 decades of experience in training child health researchers, and specific experience in training investigators in methods of comparative effectiveness research in an ARHQ-funded program. It will draw from an extensive and diverse pool of applicants across many disciplines (both MD and PhD faculty), from Harvard-affiliated institutions and across the country, who seek to begin their careers with intensive mentorship and support. The program will enroll 12 scholars for 2 or 3 years of support over the 5-year project period. The program's leadership team and faculty bring particular expertise in the novel use of health information technology across platforms and organizations to facilitate learning through research. The faculty also includes national experts in health system improvement and implementation science. We will leverage all of these resources to ensure: 1) structured, robust, and tailored mentoring in methods of patient centered comparative effectiveness research, including use of patient reported outcomes measures for children; 2) parent (and patient) engagement in the development and oversight of the career development program as well as the research of each participating scholar; 3) a broad variety of health systems for children with whom relevant research can be conducted; and, 4) partnerships with nationally-regarded organizations focused on rapid implementation of changes in practice based on the best current evidence. The program will have a particular focus on research to close the gaps in health for disadvantaged populations by improving health care delivery and community-based interventions. Its leadership and structure will not only accelerate the successful research careers of the enrolled scholars, but also align those careers with the needs of patients, health care delivery systems, and communities. In so doing, these individuals will provide the evidence for shared clinical decisions and effective community-based interventions that will bring us closer to the goal of improved health for individual children and populations.